Invited review: Unlocking the biological potential of dairy calves through elevated and ad libitum milk feeding

The nutritional management of preweaning dairy calves has changed significantly in recent decades, shifting from restricted milk feeding to elevated or ad libitum allowances that more closely mimic natural suckling behavior. This review critically evaluates the literature on milk allowances exceeding the traditional 10% of BW, specifically examining protocols offering 8 to 12 L/d or ad libitum access. The evidence indicates that these greater nutrient intakes, characterized by increased ME and MP supply, result in greater preweaning ADG, improved feed efficiency during the liquid-feeding phase, and enhanced structural development in calves. Additionally, behavioral indicators strongly suggest that restricted feeding protocols compromise animal welfare by inducing chronic hunger, as demonstrated by increased unrewarded visits to automated feeders and vocalizations, which are effectively reduced by elevated feeding. However, this nutritional strategy presents challenges, particularly the reduction of solid-feed intake and the associated delay in rumen development, requiring careful management of the weaning transition to prevent postweaning growth slumps. Long-term data suggest that early-life nutrient abundance triggers metabolic programming effects, potentially enhancing future lactation performance, mammary gland development, and herd longevity. This review integrates findings on growth biology, behavior, rumen development, health, economics, and lifetime productivity to provide a comprehensive framework for implementing elevated milk feeding strategies in modern dairy systems.